how to link a 2.4 blender file to the 2.7 blender version?
Have you tried to Save the old blender files into a new blender file? 

Try and open a new file in your newest version of blender. Then, just append every file from the Old blender file( of which you have problems linking) to the new blender file. Save that new file, and that should do it! It should work...